The disclosures herein relate generally to spool valves and more particularly to spool notch geometries for low effort backhoe valve applications.
Spool valves assist in controlling hydraulic fluid flow in a hydraulic system. System pressure may be for example, 3100 psi. The spool valve function is to provide a desired balance in the system between pressure control and flow control. To accomplish this balance, a spool valve includes a plurality of notched lands and adjacent neck portions. There are notches provided to maintain pressure control and notches provided to maintain flow control. The spool valve moves in a fluid chamber so that the notches cooperate with surfaces of the chamber to maintain the pressure control and flow control by metering fluid flow through the chamber.
U.S. Pat. No. 4,862,920 discloses a spool for a spool valve. The spool includes at least one annular land having at least three intersecting notches in a side surface thereof. The form of each notch is non-cylindrical at its intersection with an adjacent notch.
In construction machinery, for example, to control the basic operation of the backhoe functions in a loader/backhoe machine, requires the use of a hydraulic system having a control valve capable of operating the desired functions with minimal effort exerted by the operator and maximum fine controllability by the valve components. The valve utilizes a spool which, when operated in a certain manner, directs hydraulic flow to other components in the system to control basic backhoe operations when desired. The spool has incorporated characteristics that define its respective control of flow with the output being shifting effort and flow metering capability. These characteristics are defined by the notches incorporated into the spool which typically are machined into the land locations.
Therefore, what is needed is a spool notch geometry which reduces effort exerted by the backhoe operator to the extent that the operator can feel the machine operations better, such as finding buried pipe, by reducing the effort such that the effort caused by flow forces in the valve are minimized and do not mask the true feel of the machine.
One embodiment, accordingly, provides a spool including notch geometries which provide a fine tuned feel for more precise operation of hydraulic machinery. To this end, a spool valve includes a pressure control portion and a pair of flow control portions. Each flow control portion is adjacent to, and on opposite sides of, the pressure control portion. A first plurality of opposed notches are formed in the pressure control portion. The first plurality of notches have a first geometry. A second plurality of opposed notches are formed in each flow control portion. The second plurality of notches include at least one notch of a second geometry, different from the first geometry, and at least one notch of a third geometry, different from the first and second geometries.
A principal advantage of this embodiment is that the combination of notch geometries reduces the effort exerted by the operator to the extent that the operator can feel the machine operations better.